Method of operating an electroless plating apparatus

ABSTRACT

A method of operating an electroless plating apparatus is disclosed. The operating method includes: storing in the electroless plating apparatus an order of priority of the plurality of processes which has been predetermined based on a stability of a processed substrate with respect to pure water; supplying pure water into the holder storage bath when any of the plurality of processing baths malfunctions; determining whether or not a relieving process can be performed, the relieving process being a process of performing a higher-priority process on a substrate; if the relieving process can be performed, performing the relieving process and then immersing the substrate holder holding the substrate in the pure water in the holder storage bath; and if the relieving process cannot be performed, immersing the substrate holder, holding the substrate, in the pure water held in the holder storage bath without performing the relieving process.

CROSS REFERENCE TO RELATED APPLICATION

This document claims priority to Japanese Patent Application Number 2014-228273 filed Nov. 10, 2014, the entire contents of which are hereby incorporated by reference.

BACKGROUND

An electroless plating apparatus is known as a substrate processing apparatus for processing a substrate, such as a wafer. Electroless plating is a technique of forming a metal film on the substrate by chemically reducing metal ions in a plating solution without passing an electric current through the plating solution.

FIG. 9 is a view showing an electroless plating apparatus. As shown in FIG. 9, the electroless plating apparatus includes a frame 110, loading ports 112 on which wafer cassettes, each accommodating substrates W (e.g., wafers) therein, are placed, an operation controller 113 for controlling operations of the electroless plating apparatus, and an aligner 114 for aligning an orientation flat or a notch of a substrate W in a predetermined direction. The electroless plating apparatus further includes a spin-rinse-drier (SRD) 116 for drying a plated substrate W by rotating it at a high speed, a holder storage bath 118 for storing a plurality of substrate holders 117 in a vertical position, a substrate loader 120 in which a substrate W, to be plated, is loaded onto a substrate holder 117 and a plated substrate W is taken out of a substrate holder 117, and a substrate transport robot 122 for transporting a substrate W.

A moving mechanism 115 is installed along an arrangement direction of the loading ports 112. The substrate transport robot 122 is installed on the moving mechanism 115. The aligner 114 is disposed adjacent to the moving mechanism 115. The substrate transport robot 122 is configured to move on the moving mechanism 115, access the wafer cassettes set on the loading ports 112, take a substrate W, to be plated, out of the wafer cassette, and transfer the substrate W to the substrate loader 120.

In the frame 110, there are disposed a pre-cleaning unit 126 for pre-cleaning a surface of a substrate W (e.g., removing a copper oxide formed on the surface of the substrate W), and a nuclei forming unit 128 for activating the surface of the substrate W (e.g., forming palladium nuclei on the surface of the substrate W). The pre-cleaning unit 126 includes a pre-cleaning bath 126 a for storing a pre-cleaning liquid for pre-cleaning the surface of the substrate W, and a first rinsing bath 126 b for cleaning the substrate W, which has been immersed in the pre-cleaning liquid, with a cleaning liquid (e.g., pure water). The nuclei forming unit 128 includes a nuclei forming bath 128 a for forming palladium nuclei on the surface of the substrate W, and a second rinsing bath 128 b for cleaning the substrate W, on which the palladium nuclei have been formed, with a cleaning liquid (e.g., pure water).

The electroless plating apparatus further includes a first plating unit 130 for forming a first metal film, e.g., a cobalt (Co) film, on the surface of the substrate W by electroless plating, and a second plating unit 132 for forming a second metal film, e.g., a gold (Au) film, on the first metal film by electroless plating. The first plating unit 130 includes a first plating bath 130 a for storing a plating solution, such as a cobalt plating solution, and a third rinsing bath 130 b for cleaning the substrate W, which has been immersed in the plating solution held in the first plating bath 130 a, with a cleaning liquid (e.g., pure water).

The second plating unit 132 includes a second plating bath 132 a for storing a plating solution, such as a gold plating solution, and a fourth rinsing bath 132 b for cleaning the substrate W, which has been immersed in the plating solution held in the second plating bath 132 a, with a cleaning liquid (e.g., pure water).

An example of a process of plating a substrate W with use of the above-described electroless plating apparatus will be described with reference to FIGS. 10A through 10C. FIGS. 10A through 10 e are schematic views each showing a cross section of a substrate W. In the example illustrated in FIG. 10A, the substrate W, to be processed, has a photoresist 149 formed on an underlying metal film 148, and further has a copper film 150 formed in an opening of the photoresist 149. First, the substrate W is immersed in the pre-cleaning liquid retained in the pre-cleaning bath 126 a to remove a copper oxide from a surface of the copper film 150. Thereafter, the substrate W is rinsed in the first rinsing bath 126 b.

Next, palladium (Pd) nuclei are formed on the copper film 150 in the nuclei forming bath 128 a, and the substrate W is then rinsed in the second rinsing bath 128 b. Next, the substrate W is immersed in the cobalt (Co) plating solution in the first plating bath 130 a to form a cobalt film 151 on the surface of the copper film 150 (see FIG. 10B). Thereafter, the substrate W is rinsed in the third rinsing bath 130 b. The substrate W is then immersed in the gold (Au) plating solution in the second plating bath 132 a to form a gold film 152 on the cobalt film 151 (see FIG. 10C). Thereafter, the substrate W is rinsed in the fourth rinsing bath 132 b.

If any of the pre-cleaning bath 126 a, the nuclei forming bath 128 a, the first plating bath 130 a, and the second plating bath 132 a malfunctions, it is necessary to stop processing of the substrate W and to relieve the substrate W. A possible solution for relieving the substrate W is to immerse the substrate W, which has been processed in any of the pre-cleaning bath 126 a, the nuclei forming bath 128 a, the first plating bath 130 a, and the second plating bath 132 a, in the cleaning liquid (i.e., pure water) in any of the rinsing baths 126 b, 128 b, 130 b, 132 b.

However, a stability of the substrate W with respect to pure water depends on a material forming an exposed surface of the substrate W. Therefore, when the substrate W with a low stability is immersed in pure water in the rinsing bath, the substrate W may become defective. For example, when palladium nuclei are formed on the surface of the copper film 150, an exposed surface of the copper film 150 is formed from copper (Cu) and palladium. If such substrate W is immersed in the pure water, the copper having small ionization energy is dissolved in the pure water. As a result, it becomes extremely difficult to relieve the substrate W.

SUMMARY OF THE INVENTION

According to an embodiment, there is provided an operating method of an electroless plating apparatus which can reduce the number of substrates which become defective when any of processing baths, including a plating bath, malfunctions.

Embodiments, which will be described below, relate to an operating method of an electroless plating apparatus for plating a surface of a substrate, such as a wafer.

In an embodiment, there is provided a method of operating an electroless plating apparatus having a substrate holder for holding a substrate, a plurality of processing baths for performing a plurality of processes including electroless plating, and a holder storage bath for storing the substrate holder when holding no substrate, comprising: storing in the electroless plating apparatus an order of priority of the plurality of processes which has been predetermined based on a stability of a processed substrate with respect to pure water; supplying pure water into the holder storage bath when any of the plurality of processing baths malfunctions; determining whether or not a relieving process can be performed, the relieving process being a process of performing a higher-priority process on a substrate; if the relieving process can be performed, performing the relieving process and then immersing the substrate holder holding the substrate in the pure water in the holder storage bath; and if the relieving process cannot be performed, immersing the substrate holder, holding the substrate, in the pure water held in the holder storage bath without performing the relieving process.

In an embodiment, the pure water is deaerated water having a low concentration of dissolved oxygen.

In an embodiment, the relieving process is an electroless plating process of forming a metal film, having a thickness larger than a preset target thickness, on a surface of the substrate.

In an embodiment, the metal film is a cobalt film.

In an embodiment, the plurality of processes include pre-cleaning of the substrate, an activation process of the substrate, and electroless plating of the substrate.

According to the embodiments described above, the substrate, in a state such that the stability of the substrate with respect to pure water is as high as possible, is immersed in pure water in the holder storage bath. As a result, the number of substrates which become defective can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view schematically showing an embodiment of an electroless plating apparatus;

FIG. 2 is a view showing a substrate holder;

FIG. 3 is a view showing a substrate which is held by slits of a holding arm;

FIG. 4 is a schematic view showing a pure water supply and discharge mechanism;

FIG. 5 is a top view of a holder storage bath;

FIG. 6 is a view showing an order of priority of processes;

FIG. 7A, FIG. 7B, FIG. 7C, and FIG. 7D are views showing processes of relieving substrates when a second plating bath malfunctions;

FIG. 8A, FIG. 8B, FIG. 8C, and FIG. 8D are views showing processes of relieving substrates when a nuclei forming bath malfunctions;

FIG. 9 is a view showing an electroless plating apparatus; and

FIG. 10A, FIG. 10B, and FIG. 10C are schematic views each showing a cross section of a substrate.

DESCRIPTION OF EMBODIMENTS

Embodiments will now be described with reference to the drawings. The same reference numerals are denoted in FIGS. 1 through 8 to refer to the same or corresponding elements, and duplicate descriptions thereof will be omitted.

FIG. 1 is a plan view schematically showing an embodiment of an electroless plating apparatus. This electroless plating apparatus is a substrate processing apparatus which can perform various types of processes on a substrate. As shown in FIG. 1, the electroless plating apparatus includes a frame 1, loading ports 2 on which wafer cassettes, each accommodating substrates W (e.g., wafers) therein, are placed, an operation controller 3 for controlling operations of the electroless plating apparatus, and an aligner 4 for aligning an orientation flat or a notch of a substrate W in a predetermined direction. The electroless plating apparatus further includes a spin-rinse-drier (SRD) 6 for drying a plated substrate W by rotating it at a high speed, a holder storage bath 14 for storing a plurality of substrate holders 42 in a vertical position, a substrate loader 10 in which a substrate W, to be plated, is loaded onto a substrate holder 42 and a plated substrate W is taken out of a substrate holder 42, and a substrate transport robot 12 for transporting a substrate W. The holder storage bath 14 is configured to be able to accommodate, for example, thirty-seven substrate holders 42.

A moving mechanism 5 is installed along an arrangement direction of the loading ports 2. The substrate transport robot 12 is installed on the moving mechanism 5. The aligner 4 is disposed adjacent to the moving mechanism 5. The substrate transport robot 12 is configured to move on the moving mechanism 5, access the wafer cassettes set on the loading ports 2, take a substrate W, to be plated, out of the wafer cassette, and transfer the substrate W to the substrate loader 10.

In the frame 1, there are disposed a pre-cleaning unit 16 for pre-cleaning a surface of the substrate W (e.g., removing a copper oxide formed on a surface of the substrate W), and a nuclei forming unit 18 for activating the surface of the substrate W (e.g., forming palladium nuclei). The pre-cleaning unit 16 includes a pre-cleaning bath 16 a for storing a pre-cleaning liquid for pre-cleaning the surface of the substrate W, and a first rinsing bath 16 b for cleaning the substrate W, which has been immersed in the pre-cleaning liquid, with a cleaning liquid (e.g., pure water). The pre-cleaning bath 16 a is configured to accommodate one substrate holder 42, and the first rinsing bath 16 b is also configured to accommodate one substrate holder 42. The nuclei forming unit 18 includes a nuclei forming bath 18 a for forming palladium nuclei on the surface of the substrate W, and a second rinsing bath 18 b for cleaning the substrate W, on which the palladium nuclei have been formed, with a cleaning liquid (e.g., pure water). The nuclei forming bath 18 a is configured to accommodate one substrate 42, and the second rinsing bath 18 b is also configured to accommodate one substrate holder 42.

The electroless plating apparatus further includes a first plating unit 20 for forming a first metal film, e.g., a cobalt (Co) film, on the surface of the substrate W by electroless plating, and a second plating unit 24 for forming a second metal film, e.g., gold (Au) film, on the first metal film by electroless plating. The first plating unit 20 includes a first plating bath 20 a for storing a plating solution, such as a cobalt plating solution, and a third rinsing bath 20 b for cleaning the substrate W, which has been immersed in the plating solution held in the first plating bath 20 a, with a cleaning liquid (e.g., pure water). The first plating bath 20 a is configured to accommodate twenty-five substrate holders 42, and the third rinsing bath 20 b is configured to accommodate one substrate holder 42.

The second plating unit 24 includes a second plating bath 24 a for storing a plating solution, such as a gold plating solution, and a fourth rinsing bath 24 b for cleaning the substrate W, which has been immersed in the plating solution held in the second plating bath 24 a, with a cleaning liquid (e.g., pure water). The second plating bath 24 a is configured to accommodate ten substrate holders 42. The fourth rinsing bath 24 b is configured to accommodate one substrate holder 42. The pre-cleaning unit 16, the nuclei forming unit 18, the first plating unit 20, the second plating unit 24, and the holder storage bath 14 are arranged in this order in series. Hereinafter, the pre-cleaning bath 16 a, the nuclei forming bath 18 a, the first plating bath 20 a, and the second plating bath 24 a may be referred to as processing baths, respectively.

Each of the first plating unit 20 and the second plating unit 24 includes an overflow bath (not shown). The plating solution overflows a side wall of the first plating bath 20 a into the overflow bath, and is returned through a circulation line (not shown) to the first plating bath 20 a. Similarly, the plating solution overflows a side wall of the second plating bath 24 a into the overflow bath, and is returned through a circulation line (not shown) to the second plating bath 24 a. Each of the circulation lines is provided with a filter and a plating solution temperature regulator.

The substrate loader 10 is disposed adjacent to the holder storage bath 14. The substrate loader 10 includes a table 26 on which the substrate holder 42 is placed in a horizontal position, and a substrate-holder tilting mechanism 28 for raising and laying down the substrate holder 42. The substrate-holder tilting mechanism 28 is disposed outside the table 26. The substrate-holder tilting mechanism 28 is configured to change the substrate holder 42 from a vertical position to a horizontal position and place the substrate holder 42 onto the table 26. The substrate W is loaded onto and removed from the substrate holder 42 on the table 26.

The electroless plating apparatus includes a transporter 30 for transporting the substrate holder 42, holding the substrate W, in a horizontal direction. The transporter 30 includes a fixed base 40 extending horizontally from the substrate loader 10 to the pre-cleaning unit 16, an arm 32 configured to be movable horizontally on the fixed base 40, and a gripper 34 mounted to the arm 32. A linear motor or a rack and pinion may be used as a driving source for horizontally moving the arm 32. The gripper 34 is configured to be able to grip the substrate holder 42.

The substrate holder 42 will now be described with reference to FIG. 2. FIG. 2 is a view of the substrate holder 42. As shown in FIG. 2, the substrate holder 42 has projecting portions 46, 46 which project outwardly. A support arm 45 extends between these projecting portions 46, 46. Two holding arms 44, 44 for gripping a substrate W are secured to the support arm 45. The transporter 30 is configured to transport the substrate holder 42 with the gripper 34 gripping the support arm 45.

Each holding atm 44 has a first slit 44 a, a second slit 44 b, and a third slit 44 c. FIG. 3 is a view showing the substrate W which is held by the slits 44 a to 44 c of each of the holding arms 44. Only one of the holding arms 44 is shown in FIG. 3. As shown in FIG. 3, a periphery of the substrate W is inserted into the slits 44 a to 44 c, whereby the substrate W is held by the substrate holder 42. As shown in FIG. 2, the substrate W is slid from a position shown by a dotted line to a position shown by a solid line, so that the periphery of the substrate W is held by the slits 44 a to 44 c of the two holding arms 44, 44. The loading of the substrate W onto the substrate holder 42 is performed by the substrate transport robot 12 shown in FIG. 1 or a substrate sliding mechanism (not shown) mounted to the table 26.

Operations of the electroless plating apparatus will now be described with reference to FIG. 1. First, the substrate holder 42 in the vertical position is taken out of the holder storage bath 14 by a bidirectional lifter 59 disposed adjacent to the holder storage bath 14. The bidirectional lifter 59 is configured to elevate and lower the substrate holder 42 and horizontally move the substrate holder 42. The bidirectional lifter 59 can take out any one of the substrate holders 42 arranged in the holder storage bath 14. The bidirectional lifter 59 transfers the substrate holder 42 to the transporter 30, and the transporter 30 transfers the substrate holder 42 to the substrate-holder tilting mechanism 28 of the substrate loader 10. The substrate-holder tilting mechanism 28 of the substrate loader 10 changes the substrate holder 42 from the vertical position to the horizontal position, and places the substrate holder 42 onto the table 26.

The substrate transport robot 12 takes one substrate W out of the wafer cassette mounted on one of the loading ports 2, and places the substrate W onto the aligner 4. The aligner 4 aligns an orientation flat or a notch of the substrate W in a predetermined direction. Thereafter, the substrate transport robot 12 removes the substrate W from the aligner 4, and inserts the substrate W into the substrate holder 42 on the table 26. More specifically, the substrate transport robot 12 horizontally moves the substrate W to a predetermined position, and slides the substrate W from the position shown by the dotted line in FIG. 2 to the position shown by the solid line so as to insert the substrate W into the slits 44 a to 44 c of the holding arm 44, thereby loading the substrate W onto the substrate holder 42.

Next, the substrate-holder tilting mechanism 28 changes the substrate holder 42 from the horizontal position to the vertical position. The gripper 34 of the arm 32 grips the substrate holder 42 in the upright position, and the transporter 30 moves the substrate holder 42 to a predetermined position above the pre-cleaning bath 16 a. A bidirectional lifter 60 is provided adjacent to the pre-cleaning bath 16 a. The bidirectional lifter 60 is configured to elevate and lower the substrate holder 42 and horizontally move the substrate holder 42.

The bidirectional lifter 60 receives the substrate holder 42 from the transporter 30, and lowers the substrate holder 42 to immerse the substrate W, held by the substrate holder 42, in the pre-cleaning liquid in the pre-cleaning bath 16 a. The surface of the substrate W is pre-cleaned with the pre-cleaning liquid. This pre-cleaning is, for example, a process of removing the copper oxide formed on the surface of the substrate W, and is referred to as a pre-cleaning process. After pre-cleaning of the substrate W, the bidirectional lifter 60 elevates the substrate holder 42 to pull the substrate W out of the pre-cleaning liquid.

The bidirectional lifter 60 horizontally moves the substrate holder 42 to the first rinsing bath 16 b adjacent to the pre-cleaning bath 16 a, and lowers the substrate holder 42 to immerse the substrate W in the cleaning liquid (pure water) in the first rinsing bath 16 b, so that the substrate W is cleaned (i.e., rinsed) with the cleaning liquid. After the cleaning of the substrate W, the bidirectional lifter 60 elevates the substrate holder 42 to pull the substrate W out of the cleaning liquid in the first rinsing bath 16 b.

The transporter 30 receives the substrate holder 42 from the bidirectional lifter 60, and moves the substrate holder 42 to a predetermined position above the nuclei forming bath 18 a. A bidirectional lifter 61 is provided adjacent to the nuclei forming bath 18 a. This bidirectional lifter 61 is configured to elevate and lower the substrate holder 42 and horizontally move the substrate holder 42.

The bidirectional lifter 61 receives the substrate holder 42 from the transporter 30, and lowers the substrate holder 42 to place the substrate W, held by the substrate holder 42, in the nuclei forming bath 18 a. In this nuclei forming bath 18 a, nuclei (e.g., palladium nuclei) necessary for deposition of a metal film are formed on the surface of the substrate W. Such a process is referred to as an activation process (or catalyst forming process). After the activation process, the bidirectional lifter 61 elevates the substrate holder 42 to pull the substrate W out of the nuclei forming bath 18 a. The bidirectional lifter 61 then horizontally moves the substrate holder 42 to the second rinsing bath 18 b adjacent to the nuclei forming bath 18 a, and lowers the substrate holder 42 to immerse the substrate W in the cleaning liquid (pure water) in the second rinsing bath 18 h. The substrate W is cleaned (i.e., rinsed) with the cleaning liquid. After the cleaning of the substrate W, the bidirectional lifter 61 elevates the substrate holder 42 to pull the substrate W out of the cleaning liquid in the second rinsing bath 18 b.

The transporter 30 receives the substrate holder 42 from the bidirectional lifter 61, and moves the substrate holder 42 to a predetermined position above the first plating bath 20 a. A substrate-holder transporting mechanism 70 is provided adjacent to the first plating bath 20 a. The substrate-holder transporting mechanism 70 is configured to horizontally move the substrate holder 42 while keeping the substrate W immersed in the plating solution in the first plating bath 20 a. A unidirectional lifter 65 is provided outside the substrate-holder transporting mechanism 70. The unidirectional lifter 65 is configured to elevate and lower the substrate holder 42.

The unidirectional lifter 65 receives the substrate holder 42 from the transporter 30, and lowers the substrate holder 42 to transfer the substrate holder 42 to the substrate-holder transporting mechanism 70. The substrate-holder transporting mechanism 70 advances the substrate holder 42 from a holder put-in position “IN” to a holder takeout position “OUT” while keeping the entirety of the substrate W immersed in the plating solution in the first plating bath 20 a. While the substrate W thus moves in the plating solution, electroless plating is performed on the surface of the substrate W. This electroless plating is, for example, cobalt (Co) plating (i.e., a cobalt plating process).

A bidirectional lifter 62 is provided outside the substrate-holder transporting mechanism 70. This bidirectional lifter 62 elevates the substrate holder 42 that has reached the holder takeout position “OUT” to pull the substrate W out of the plating solution. The bidirectional lifter 62 then horizontally moves the substrate holder 42 to the third rinsing bath 20 b adjacent to the first plating bath 20 a, and lowers the substrate holder 42 to immerse the substrate W in a cleaning liquid (pure water) in the third rinsing bath 20 b. The substrate W is cleaned (i.e., rinsed) with the cleaning liquid. After the cleaning of the substrate W, the bidirectional lifter 62 elevates the substrate holder 42 to pull the substrate W out of the cleaning liquid in the third rinsing bath 20 b.

The transporter 30 receives the substrate holder 42 from the bidirectional lifter 62, and horizontally moves the substrate holder 42 to a predetermined position above the second plating bath 24 a. A substrate-holder transporting mechanism 71 is provided adjacent to the second plating bath 24 a. A unidirectional lifter 66 is provided outside the substrate-holder transporting mechanism 71.

The unidirectional lifter 66 receives the substrate holder 42 from the transporter 30, and lowers the substrate holder 42 to transfer the substrate holder 42 to the substrate-holder transporting mechanism 71. The substrate-holder transporting mechanism 71 advances the substrate holder 42 from a holder put-in position “IN” to a holder takeout position “OUT” while keeping the entirety of the substrate W immersed in the plating solution in the second plating bath 24 a. While the substrate W thus moves in the plating solution, electroless plating is performed on the surface of the substrate W. This electroless plating is, for example, gold (Au) plating (i.e., a gold plating process). In this manner, two types of plating processes are sequentially performed on the substrate W in the first plating unit 20 and the second plating unit 24, so that different metal films are sequentially formed on the surface of the substrate W. In this embodiment, since the gold plating process is performed after the cobalt plating process, the gold film is formed on the cobalt film.

A bidirectional lifter 63 is provided outside the substrate-holder transporting mechanism 71. The bidirectional lifter 63 elevates the substrate holder 42 that has reached the holder takeout position “OUT” to pull the substrate W out of the plating solution. The bidirectional lifter 63 then horizontally moves the substrate holder 42 to the fourth rinsing bath 24 b adjacent to the second plating bath 24 a, and lowers the substrate holder 42 to immerse the substrate W in the cleaning liquid (pure water) in the fourth rinsing bath 24 b. The substrate W is cleaned (i.e., rinsed) with the cleaning liquid. After the cleaning of the substrate W, the bidirectional lifter 63 elevates the substrate holder 42 to pull the substrate W out of the cleaning liquid in the fourth rinsing bath 24 b. The transporter 30, the bidirectional lifters 59, 60, 61, 62, 63, the unidirectional lifters 65, 66, and the substrate-holder transporting mechanisms 70, 71 may collectively be referred to as transporting device.

The transporter 30 receives the substrate 42 from the bidirectional lifter 63, horizontally moves the substrate holder 42, and transfers the substrate holder 42 to the substrate-holder tilting mechanism 28. The substrate-holder tilting mechanism 28 places the substrate holder 42 onto the table 26. The substrate transport robot 12 removes the substrate W from the substrate holder 42 by sliding the substrate W from the position shown by the solid line in FIG. 2 to the position shown by the dotted line.

Thereafter, the substrate transport robot 12 transports the substrate W to the spin-rinse-dryer 6. The spin-rinse-dryer 6 dries the substrate W by rotating it at a high speed. The substrate transport robot 12 removes the dried substrate W from the spin-rinse-dryer 6 and returns it to the wafer cassette on the loading port 2, whereby processing of the substrate W is completed.

In a case where any of the processing baths 16 a, 18 a, 20 a, and 24 a malfunctions when the electroless plating apparatus is in operation, pure water is supplied into the holder storage bath 14. Specifically, the electroless plating apparatus includes a pure water supply and discharge mechanism 35 which supplies pure water into the holder storage bath 14 and discharges the pure water from the holder storage bath 14. The operation controller 3 is configured to control an operation of the pure water supply and discharge mechanism 35.

The pure water supply and discharge mechanism 35 will be described with reference to FIG. 4. FIG. 4 is a schematic view showing the pure water supply and discharge mechanism 35. As shown in FIG. 4, the pure water supply and discharge mechanism 35 includes a supply line 75 coupled to a bottom of the holder storage bath 14, an ON-OFF valve 76 coupled to the supply line 75, and a discharge line 77 coupled to the bottom of the holder storage bath 14. The supply line 75 is coupled to a pure water supply line (not shown). When the ON-OFF valve 76 is opened, the pure water is supplied through the supply line 75 into the holder storage bath 14. The pure water is discharged from the holder storage bath 14 through the discharge line 77.

FIG. 5 is a top view of the holder storage bath 14. The holder storage bath 14 is configured to be able to accommodate all of the substrate holders 42 which are present in the electroless plating apparatus, and has the same number of compartments 36 as the number of processes to be performed on the substrate W (in this embodiment, four processes, i.e., the pre-cleaning process, the activation process, the cobalt plating process, and the gold plating process). The compartments 36 are completely separated by partitions 37 so that the pure water does not flow between the compartments 36. The number of substrate holders 42, which can be accommodated in each of the compartments 36, corresponds to the maximum number of substrate holders 42 which can be accommodated in each of the processing baths 16 a, 18 a, 20 a, 24 a, respectively. The pure water supply and discharge mechanism 35 is configured to supply the pure water into the compartments 36. When a predetermined amount of the pure water is held in each compartment 36, the supply of the pure water is stopped. The pure water to be supplied into the holder storage bath 14 may preferably be deaerated water having a low concentration of dissolved oxygen.

When a malfunction has occurred in any one of the processing baths 16 a, 18 a, 20 a, 24 a, the substrate W, together with the substrate holder 42, is transported to the holder storage bath 14 by the transporting device, and is immersed in the pure water retained in the holder storage bath 14. However, as described above, the stability of the substrate W with respect to the pure water varies depending on a material forming an exposed surface of the substrate W. Therefore, if the substrate W with a low stability is immersed in the pure water, the substrate W becomes defective. Hereinafter, the stability of the substrate W with respect to the pure water will be described.

When palladium nuclei are formed on the surface of the copper film (see the symbol 150 in FIGS. 10A through 10C), the exposed surface of the substrate W is constituted by copper (Cu) and palladium. When such substrate W is immersed in the pure water, copper having small ionization energy is dissolved in the pure water. As a result, it becomes extremely difficult to relieve the substrate W. Therefore, the stability of the substrate W having the copper film and palladium nuclei formed thereon with respect to the pure water is extremely low.

When a substrate W plated with cobalt is immersed in the pure water, a surface of the cobalt film is oxidized, and as a result, a cobalt oxide film is formed on the surface of the cobalt film. Unless the cobalt oxide film is removed, processing of the substrate W cannot be resumed after the electroless plating apparatus is returned to a normal operating condition. Therefore, the stability of the substrate W plated with cobalt with respect to the pure water is low.

When a pre-cleaned substrate W is immersed in pure water, a copper oxide is formed on the surface of the substrate W. However, by immersing the substrate W in the pre-cleaning liquid again, the copper oxide on the surface of the substrate W can be removed. Therefore, the stability of the pre-cleaned substrate W with respect to the pure water is high. A substrate W plated with gold is not adversely affected even when such a substrate W is immersed in pure water. Therefore, it is highly probable that the substrate W can be relieved. Accordingly, the stability of the substrate W plated with gold with respect to the pure water is extremely high.

The operation controller 3 has stored therein in advance an order of priority of the processes which has been determined based on the stability of a processed substrate W with respect to pure water. In this embodiment, a process with a highest priority is the gold plating process, a process with a second highest priority is the pre-cleaning process, a process with a third highest priority is the cobalt plating process, and a process with a lowest priority is the activation process. That is, the order of priority is (1) the gold plating process, (2) the pre-cleaning process, (3) the cobalt plating process, and (4) the activation process.

A method of relieving a substrate W in a case where the second plating bath 24 a malfunctions will now be described with reference to FIG. 6 and FIGS. 7A through 7D. FIG. 6 is a view showing the order of priority of the processes. FIGS. 7A through 7D are views showing processes of relieving substrates W when the second plating bath 24 a malfunctions.

When the second plating bath 24 a malfunctions, first, a loading of an unprocessed substrate W onto the substrate holder 42 in the substrate loader 10 is stopped. Next, the pure water supply and discharge mechanism 35 supplies the pure water into the holder storage bath 14. The operation controller 3 determines whether or not a relieving process can be performed based on the stored order of priority (i.e., (1) the gold plating process, (2) the pre-cleaning process, (3) the cobalt plating process, (4) the activation process). The relieving process is a process of performing a higher-priority process on a substrate W. If the operation controller 3 has determined that the relieving process can be performed, the relieving process is performed on the substrate W, and the substrate W is then immersed in the pure water held in the holder storage bath 14.

As shown in FIG. 7A, if the malfunction has occurred in the second plating bath 24 a during the gold plating of a substrate W, the gold plating process cannot be completed in the second plating bath 24 a. However, if the substrate W stays immersed in the plating solution, an excessive gold film is formed on the substrate W, and as a result, the substrate W should be scrapped. Thus, in order to relieve the substrate W, the substrate W in the second plating bath 24 a is transported together with the substrate holder 42 to a compartment 36 by the transporter 30, and the substrate W is immersed in the pure water in this compartment 36. As shown by dotted arrows in FIG. 7A, the substrate W may be immersed in the cleaning liquid (e.g., pure water) in the fourth rinsing bath 24 b, and the substrate W may be then transported into the compartment 36.

As shown in FIG. 7B, if the malfunction has occurred in the second plating bath 24 a during cobalt plating processing of a substrate W, the substrate W plated with cobalt cannot be transported to the second plating bath 24 a. Therefore, first, the substrate W in the first plating bath 20 a is transported to the third rinsing bath 20 b, and the substrate W is immersed in the cleaning liquid (pure water) in the third rinsing bath 20 b. Thereafter, the substrate W, together with the substrate holder 42, is transported to a compartment 36 by the transporter 30, and the substrate W is immersed in the pure water in this compartment 36. The substrate W plated with cobalt is accommodated in the compartment 36 which is different from the compartment 36 in which the substrate W plated with gold is accommodated. Since the compartments 36 are completely separated, the gold plating solution and the cobalt plating solution attached to the substrates W and the substrate holders 42 are not mixed with each other.

As shown in FIG. 7C, if the malfunction has occurred in the second plating bath 24 a during the activation process of a substrate W, the substrate W that has been processed in the nuclei forming bath 18 a is transported to the second rinsing bath 18 b, and is cleaned (i.e., rinsed) with the cleaning liquid in the second rinsing bath 18 b. Thereafter, the substrate W, together with the substrate holder 42, is transported to the first plating bath 20 a by the transporter 30, and the substrate W is plated with cobalt. According to the order of priority that has been stored in the operation controller 3, the cobalt plating process has a higher priority than the activation process. Therefore, after the activation process of the substrate W is completed, the cobalt plating process is performed on the substrate W. The stability of the substrate W plated with cobalt with respect to the pure water is higher than the stability of the substrate W that has been subjected to the activation process with respect to the pure water. Therefore, in the embodiment illustrated in FIG. 7C, the cobalt plating process is the relieving process of the substrate W.

The substrate W plated with cobalt is cleaned (or rinsed) in the third rinsing bath 20 b and is transported, together with the substrate holder 42, to the compartment 36 by the transporter 30. The substrate W is then immersed in the pure water held in this compartment 36.

As shown in FIG. 7D, if the malfunction has occurred in the second plating bath 24 a during pre-cleaning of a substrate W, the relieving process of the substrate W is not performed. That is, the activation process and the cobalt plating process are not performed on the pre-cleaned substrate W. This is because the pre-cleaning process has a higher priority than the activation process and the cobalt plating process. Therefore, the pre-cleaned substrate W, together with the substrate holder 42, is transported to a compartment 36 by the transporter 30, and is immersed in the pure water in this compartment 36. The pre-cleaned substrate W is accommodated in the compartment 36 which is different from the compartments 36 in which the substrate W plated with cobalt and the substrate W plated with gold are accommodated. As shown by a dotted arrow in FIG. 7D, the substrate W may be immersed in the cleaning liquid (or pure water) in the first rinsing bath 16 b adjacent to the pre-cleaning bath 16 a, instead of transporting the substrate W to the compartment 36.

As described above, the number of substrate holders 42, which can be accommodated in each of the compartments 36 in the holder storage bath 14, corresponds to the maximum number of substrate holders 42 which can be accommodated in each of the processing baths 16 a, 18 a, 20 a, 24 a. If the electroless plating apparatus malfunctions, the substrates W, which are being processed in the respective processing baths, are transported to the compartments 36 assigned in advance to the respective processing baths, and are accommodated in the respective compartments 36. Since the holder storage bath 14 is partitioned for each one of the processing baths, it is possible to prevent an adverse effect which could occur as a result of reactions between the substrates W and small amounts of processing solution components attached to the substrates W and the substrate holders 42 that have been subjected to different processes.

Next, a method of relieving a substrate W in a case where the nuclei forming bath 18 a malfunctions will be described with reference to FIGS. 8A through 8D. FIGS. 8A through 8D are views showing processes of relieving substrates W when the nuclei forming bath 18 a malfunctions.

If the malfunction has occurred in the nuclei forming bath 18 a, first, a loading of an unprocessed substrate W onto the substrate holder 42 in the substrate loader 10 is stopped. Next, the pure water supply and discharge mechanism 35 supplies the pure water into the holder storage bath 14. The operation controller 3 determines whether or not a relieving process can be performed based on the stored order of priority. The relieving process is a process of performing a higher-priority process on a substrate W. If the operation controller 3 has determined that the relieving process can be performed, the relieving process is performed on the substrate W, and the substrate W is then immersed in the pure water held in the holder storage bath 14.

As shown in FIG. 8A, if the malfunction has occurred in the nuclei forming bath 18 a during the gold plating process of the substrate W, the gold plating process is allowed to be completed. The substrate W plated with gold is transported, together with the substrate holder 42, to a compartment 36 by the transporter 30, and the substrate W is then immersed in the pure water in this compartment 36. As shown by dotted arrows in FIG. 8A, the substrate W may be immersed in the cleaning liquid (or pure water) in the fourth rinsing bath 24 b, and the substrate W may be then transported to the compartment 36.

As shown in FIG. 8B, if the malfunction has occurred in the nuclei forming bath 18 a during the cobalt plating process of the substrate W, the cobalt plating process is allowed to be completed, because the cobalt plating process is not affected by the malfunction of the nuclei forming bath 18 a. The substrate W in the first plating bath 20 a is transported to the third rinsing bath 20 b, and is immersed in the cleaning liquid (or pure water) in the third rinsing bath 20 b. Thereafter, the substrate W, together with the substrate holder 42, is transported to the second plating bath 24 a by the transporter 30, and the substrate W is immersed in the gold plating solution so that the substrate W is plated with gold. The stability of the substrate W plated with gold with respect to pure water is higher than the stability of the substrate W plated with cobalt with respect to pure water. Therefore, in the embodiment illustrated in FIG. 8B, the gold plating process is the relieving process of the substrate W.

The substrate W plated with gold is transported to the compartment 36 by the transporter 30, and is immersed in the pure water held in the compartment 36. As shown by dotted arrows in FIG. 8B, the substrate W may be immersed in the cleaning liquid (or pure water) in the fourth rinsing bath 24 b, and the substrate W may be then transported to the compartment 36.

As shown in FIG. 8C, if the malfunction has occurred in the nuclei forming bath 18 a during the activation process of the substrate W, the substrate W cannot go to the next process step as long as the activation process of the substrate W is completed. Therefore, in this case, the substrate W is transported to a compartment 36 without performing the relieving process. The substrate W is accommodated in this compartment 36 which is different from compartments 36 that accommodate substrates W that have been subjected to the processes, other than the activation process.

As shown in FIG. 8D, if the malfunction has occurred in the nuclei forming bath 18 a during the pre-cleaning process of the substrate W, the substrate W cannot go to the next process step, as long as the pre-cleaning process of the substrate W is completed. Therefore, in this case, the substrate W is transported to a compartment 36 without performing the relieving process. The substrate W is accommodated in this compartment 36 which is different from compartments 36 that accommodate substrates W that have been subjected to the processes, other than the pre-cleaning process. As shown by dotted arrow in FIG. 8D, the substrate W may be immersed in the cleaning liquid in the first rinsing bath 16 b adjacent to the pre-cleaning bath 16 a without transporting the substrate W to the compartment 36.

According to this embodiment, the substrate W is immersed in the pure water in the holder storage bath 14 in a state such that the stability of the substrate W with respect to the pure water is as high as possible. As a result, it is possible to reduce the number of substrates W which become defective.

If the substrate W is pulled out of the pure water in the holder storage bath 14, is dried in the spin-rinse-dryer 6, and is then returned to the wafer cassette by the substrate transport robot 12, the operations of the substrate transport robot 12 increase. As a result, relieving of all substrates W is delayed. Therefore, the substrate W, with the substrate holder 42 holding the substrate W, is stored in the pure water in the holder storage bath 14.

When the electroless plating apparatus is returned to the normal operating condition, the pure water held in the holder storage bath 14 is discharged through the discharge line 77, and processing of the substrates W is then resumed.

When the substrate W is plated with cobalt as the relieving process of the substrate W, it is preferable to form a cobalt film having a larger thickness than a preset target thickness. In the case where a plurality of substrates W are plated with cobalt, plating times of these substrates W are controlled such that cobalt films having the same thickness are formed on all of the substrates W. Specifically, the operation controller 3 controls transporting times of the substrates W in the substrate-holder transporting mechanism 70 so that immersion times of all of the substrates W in the plating solution are the same.

When the substrate W plated with cobalt is immersed in pure water, a cobalt oxide film is formed on the surface of the substrate W. Therefore, after the relieving process of the substrate W, the substrate W is transported to a cobalt oxide film removing device 80 (see FIG. 1). The cobalt oxide film removing device 80 is a device capable of removing the cobalt oxide film by, for example, a hydrogen reduction method. Specifically, the substrate W is heated in a hydrogen atmosphere formed in the cobalt oxide film removing device 80, so that the cobalt oxide film is removed. After the removal of the cobalt oxide film, the substrate W is transported to an etching device 81 (see FIG. 1). The cobalt film formed thicker than the target thickness is etched so as to have the target thickness. Etching of the substrate W may be performed by an etching device (not shown) which is provided outside the electroless plating apparatus. The etched substrate W is transported to the second plating bath 24 a, and is then plated with gold.

A plating reaction depends on a temperature of a plating solution. If a heater for heating the plating solution malfunctions, the temperature of the plating solution is gradually lowered, and a plating rate is also lowered with a decrease in the temperature. As a result, a thickness of a metal film formed on a substrate W cannot be estimated from a plating time of the substrate W. Thus, it is desirable to measure the thickness of the metal film formed on the substrate W by using a film-thickness measuring device 82 for measuring the thickness of the metal film. The film-thickness measuring device 82 may be a non-contact type thickness measuring device using fluorescence X-rays. The thickness of the metal film formed on the substrate W is measured by the film-thickness measuring device 82, and a thickness to be added or to be reduced is determined based on the measured thickness of the metal film. If the measured thickness of the metal film is less than the target thickness, the substrate W is plated again. If the measured thickness of the metal film is larger than the target thickness, the metal film is etched by the etching device 81.

While the present invention has been described with reference to the embodiments thereof, it should be understood that the present invention is not limited to the particular embodiments described above, and that other modifications may be made within the technical concept of the present invention. 

What is claimed is:
 1. A method of operating an electroless plating apparatus having a substrate holder for holding a substrate, a plurality of processing baths for performing a plurality of processes including electroless plating, and a holder storage bath for storing the substrate holder when holding no substrate, comprising: storing in the electroless plating apparatus an order of priority of the plurality of processes which has been predetermined based on a stability of a processed substrate with respect to pure water; supplying pure water into the holder storage bath when any of the plurality of processing baths malfunctions; determining whether or not a relieving process can be performed, the relieving process being a process of performing a higher-priority process on a substrate; if the relieving process can be performed, performing the relieving process and then immersing the substrate holder holding the substrate in the pure water in the holder storage bath; and if the relieving process cannot be performed, immersing the substrate holder, holding the substrate, in the pure water held in the holder storage bath without performing the relieving process.
 2. The method according to claim 1, wherein the pure water is deaerated water having a low concentration of dissolved oxygen.
 3. The method according to claim 1, wherein the relieving process is an electroless plating process of forming a metal film, having a thickness larger than a preset target thickness, on a surface of the substrate.
 4. The method according to claim 3, wherein the metal film is a cobalt film.
 5. The method according to claim 1, wherein the plurality of processes include pre-cleaning of the substrate, an activation process of the substrate, and electroless plating of the substrate. 